Centos - basic knowledge

change DNS setting
/etc/resolve.conf

change host IP
/etc/sysconfig/network-script/ifcfg-eth0

change hostname
/etc/sysconfig/network

The easiest way to do it is
# system-config-network

Adding Swap Space

To add a swap file:

1. Determine the size of the new swap file in megabytes and multiply by 1024 to determine the number of blocks. For example, the block size of a 64 MB swap file is 65536.
   
2. At a shell prompt as root, type the following command with count being equal to the desired block size:
   

   dd if=/dev/zero of=/swapfile bs=1024 count=65536

3. Setup the swap file with the command:
   

   mkswap /swapfile

4. To enable the swap file immediately but not automatically at boot time:
   

   swapon /swapfile

5. To enable it at boot time, edit /etc/fstab to include the following entry:
   

   /swapfile          swap            swap    defaults        0 0

   The next time the system boots, it enables the new swap file.
   
6. After adding the new swap file and enabling it, verify it is enabled by viewing the output of the command cat /proc/swaps or free.

To remove the swap file:

1. First must stop the swap file created by:
   swapoff  /swapfile
2. Then delete the:
   rm -rf   /swapfile